I found this blog post after also writing today about Time Well Spent https://blog.wekan.team/2018/02/time-well-spent/index.html and production setup for Wekan https://wekan.github.io at AWS for thousands of users https://github.com/wekan/wekan/wiki/AWS .

About optimization there is DTrace talks at http://dtrace.org/blogs/bmc/2018/02/03/talks/ and related HN discussion at https://news.ycombinator.com/item?id=16303595

I do remember Randal Schwartz talking at Floss Weekly https://twit.tv/floss sometime that in his work he tries to listen developers and ask right questions to see where bottlenecks are. Is there some expensive database query, does something need to be cached, etc.